Firstly, background art relating to an inkjet recording apparatus using a liquid droplet ejecting method, and a liquid droplet ejection apparatus will be described below.
Inkjet recording apparatuses in current use are allowed to undergo displacement of a piezoelectric element etc. provided in a liquid chamber in an ink head to eject an ink in the liquid chamber from ink nozzles, in the form of ink droplets, and to adhere onto recording paper, thereby enabling printing on the recording paper. Such inkjet recording apparatuses are widely prevalent because of their cheap costs and compactness. Most of the inkjet recording apparatuses use Helmholtz resonance vibration to eject liquid droplets, as described in PTL 1. In an inkjet head using the Helmholtz resonance vibration, Helmholtz resonance vibration is excited, by a piezoelectric body, in a pressure generation chamber constituting the head so as to eject liquid droplets from ejection holes. It is known that a resonance frequency of Helmholtz resonance vibration is set in view of a fluid compliance attributable to the compressibility of an ink in a pressure generation chamber, a rigidity compliance of materials themselves for an elastic plate and an ejection hole plate each forming the pressure generation chamber, and inertance in opening of ejection holes and an ink supply port. A resonance frequency f of Helmholtz resonance vibration in the pressure generation chamber is represented by the following Equation 1. In Equation 1, a fluid compliance attributable to the compressibility of an ink in a pressure generation chamber is represented by Ci, a rigidity compliance of materials themselves for an elastic plate and an ejection hole plate each forming the pressure generation chamber is represented by Cv, inertance in an opening of an ejection hole is represented by Mn, and inertance in an ink supply port is represented by MS.f=1/(2π)×√{square root over ( )}{(Mn+MS)/(Mn×MS)(Ci+Cv)}   Equation A
Further, in a liquid droplet ejection method using Helmholtz resonance vibration, frequency components of the resonance vibration represented by Equation A are controlled to thereby control ejection of liquid droplets. That is, the resonance frequency f determined by Equation A is the maximum drive frequency of a piezoelectric body, and frequencies are controlled based on the maximum drive frequency to thereby control the operation of liquid droplet ejection.
Furthermore, besides the liquid droplet ejection method using Helmholtz resonance vibration, a liquid droplet ejecting method proposed in PTL 2 is a liquid droplet ejecting method in which an ink in a liquid column resonance-generating liquid chamber is ejected from ejection holes in a longitudinal direction of the liquid column resonance-generating liquid chamber, by utilizing a standing wave which generates in the longitudinal direction of the liquid column resonance-generating liquid chamber.
However, according to the liquid droplet ejecting method disclosed in PTL 1 using Helmholtz resonance vibration, in order to a desired resonance frequency, the accuracy of the fluid compliance for pressure generation chamber and the rigidity compliance must be increased. Unfavorably, the processing technique for pressure generation chamber has a limitation on accuracy, and it is difficult to obtain a desired resonance frequency. In addition, it is difficult to set the resonance frequency high, and thus the liquid droplet ejecting method has a problem that the liquid droplet diameter inversely proportional to the resonance frequency cannot be made small. Further, the liquid droplet ejecting method disclosed in PTL 2 has a limit to eject microscopic liquid droplets using a high frequency, because the ejection holes are disposed in the direction of propagation of the standing wave.
Next, the following describes background art relating to production methods of fine particles and fine particles using a fine particle production apparatus, in particular, toners.
Firstly, a pulverization method, which is one of toner production methods, is described by way of conventional resin fine particles. The pulverization method is a typical toner production method that has been conventionally employed, and a method in which a toner composition is melt-kneaded by a two-roll or a biaxial extruder, and the melt-kneaded product is cooled, followed by a pulverization treatment of coarse powder, a pulverization treatment of fine powder and a classification treatment, when required, a mixing treatment of external additives such as a fluidizer by a HENSCHEL MIXER, etc. In the pulverization treatment of coarse powder, a ROTOPLEX or pulverizer can be used. In the pulverization treatment of fine powder, a jet mill or turbo mill can be used. In the classification treatment, known production apparatuses such as an ELBOWJET and a variety of air classifiers can be used.
There is a spray method as one of the conventional toner production methods other than the above-mentioned pulverization method. This spray method is a method in which a toner composition is formed into liquid droplets in a vapor phase by using a single-fluid ejection hole (pressurization type ejection hole) sprayer which sprays a liquid from ejection holes by application of pressure, a multiple-fluid spray ejection hole sprayer which sprays a liquid and compressed gases in a mixed form, a rotational disc type sprayer which forms a liquid into liquid droplets by a centrifugal force using a rotating disc, or the like. In the spray method, as a spray-dry system configured to simultaneously perform spraying and drying, a commercially available device can be used, however, when an ink cannot be sufficiently dried, secondary drying such as fluidized bed drying is performed, and when necessary, mixing of external additives such as a fluidizer is performed using a HENSCHEL MIXER etc.
Further, as a conventional toner production method other than the pulverization method, there is a jet granulation method. In the jet granulation method, liquid droplets are ejected from ejection holes each having a diameter as small as the diameter of toner using a vibration generating unit, although a part of forming a liquid into droplets and solidifying the droplets is the same as in the spray method. Conventionally, some jet granulation methods have been proposed. As one of the jet granulation methods, PTL 3 proposed a toner production method, in which the inside of a pressurization chamber is pressurized to generate a liquid column from nozzles, the liquid column is broken into droplets by a weak ultrasonic vibration, and the droplets are dried and solidified to produce a toner, and a toner production apparatus therefor. Such a toner production apparatus generally includes a toner composition liquid-housing container to house a toner composition liquid to be supplied to a pressurization chamber in a liquid droplet jetting unit, and the toner composition liquid-housing container includes a stirring member which stirs the toner composition liquid housed therein to generate a flow. By generating a flow in the toner composition liquid-housing container by the stirring member, respective materials can maintain a uniformly dispersed state in the toner composition liquid, and it is possible to prevent the respective materials from being dispersed with nonuniformity in the toner composition liquid. There is disclosed a toner production apparatus in which a toner composition liquid is pressurized to form a liquid column from through holes, a weak vibration is applied to the liquid column by a vibration generating unit to excite a Rayleigh fission, thereby forming uniform liquid droplets, followed by solidifying the liquid droplets, to thereby produce toner base particles. In the method employing Rayleigh fission, a liquid is pressurized to be ejected, and thus the method has an advantage in that the vibration generating unit is only required to generate a weak vibration, and a toner composition liquid can be formed into droplets with a low voltage.
However, the toner production method proposed in PTL3 utilizes Rayleigh fission, and thus when a toner having a small diameter is produced, in order to form liquid droplets having a particle size of about two-times the inner diameter of the ejection hole, the inner diameter of the ejection hole should be made small. Further, this toner production method has a problem that the liquid is pressurized in one direction, and toner components are clogged inside the nozzle depending on the composition of the toner.
In a head part disclosed in PTL4 as a still another example of a toner production method using the jet granulation method, pulse-pressurization is performed to uniformly pressurize the entire system of toner materials stored in a toner material reservoir part for storing the toner materials, and thereby the toner materials are ejected from ejection holes. Hereinbelow, the principles of ejection of liquid droplets disclosed in PTL4 are outlined with reference to FIGS. 32A to 32E. In FIGS. 32A to 32E, pressure values inside a material reservoir part (a) are described. In the liquid droplet ejecting method disclosed in PTL4, a toner composition liquid is effected to repeatedly behave three states described below to thereby form liquid droplets intermittently. As a first state, a head part is in a state where no ejection signal is input, that is, as illustrated in FIG. 32A, in a state where no deformation occurs in a piezoelectric body (which may be referred to as piezoelectric element) (b), causing no volume change in a material reservoir part (a), and a material liquid is not ejected from an ejection hole. Next, in a second state, an ejection signal is input, the piezoelectric body (b) undergoes displacement to the inside of the material reservoir part (a), and the material reservoir part (a) decreases as illustrated in FIGS. 32B and 32C. At this time, the pressure inside the material reservoir part (a) is momentarily increased with uniformity, and the material liquid is ejected from the ejection hole. At this time, a flow of the materials is generated from the material reservoir part (a) to the side of a material housing part (not illustrated). Next, as a third state, after completion of the first time ejection of the materials, as illustrated in FIGS. 32D and 32E, application of the voltage is stopped, and the piezoelectric element (b) restores its substantially original shape. At this time, a negative pressure works in the material liquid, and the material liquid in an amount commensurate with an ejection amount is fed from a material housing part called a feeder for housing the material liquid to the material reservoir part (a).
However, since the liquid ejection method disclosed in PTL 4 is a method of momentarily pressurizing the material liquid stored in the material reservoir part (a) to intermittently eject the material liquid, there is a need to feed the material liquid reduced by a portion ejected in the third state to the material reservoir part (a) to restore the first state again where the material liquid is adequately stored. In view of the time spared for the third state and the overall production process time, a time loss occurs, and the liquid ejection method has a problem that the toner production efficiency corresponding to the time loss is reduced. Further, in the method disclosed in PTL4, generally, liquid droplets large in size are inconveniently formed, and thus, in order to obtain a dry-process toner particle, the ejection part must be made to have a small diameter or the materials must be diluted. However, when the ejection part is reduced in size, inevitably, the probability of causing clogging of a solid dispersion of a pigment which is essentially added as a toner constituent element and a releasing agent etc. added as required dramatically increases, causing a problem with production stability. In addition, when the toner material is diluted, the energy required for drying and solidifying the resulting diluent increases, which also greatly decreases the production efficiency. Furthermore, a decrease of the production efficiency prolongs the time for storing the material liquid in the material reservoir part, and a retention of the material liquid occurs, which may consequently cause sticking of the toner material fractions in a long-term production period.